ECG systems are well known, and provide information about the physiological status of a patient's heart to a physician. More specifically, so called conventional 12 lead ECG systems exist which provide twelve waveforms, called leads (lead signals), to a physician. To provide such a 12 lead ECG, ten electrodes are placed on the patient's body, and the signals from these electrodes are processed to provide twelve lead signals in a known manner. These ten electrodes include four electrodes which provide signals that are processed to generate six limb lead signals, and six electrodes which provide signals that are processed to provide precordial or chest leads.
However, there are conditions under which it is preferable or expedient to attach a limited number, (e.g. two), chest lead electrodes to a patient and to synthesize (predict) the remaining (e.g., four) chest lead signals of the six chest lead signals of the 12 lead ECG set. Such conditions include, for example, when one or more of the six standard chest lead locations on the patient's body, at which one or more of the electrodes should be placed, may be unavailable due to injury or surgery. Alternatively, it may be desirable to save time (e.g., in an emergency) to attach just two of the six standard chest lead electrodes or there may be one or more chest lead signals giving intermittent or degraded response for which it may be desirable to substitute synthesized signals. In some cases, patient comfort or the use of telemetered ECG signals may render it desirable to monitor patients with a reduced number of chest electrodes, while producing a full set of six chest lead signals. It is desirable under these conditions to still provide the full set of 6 chest lead signals by synthesizing the remaining chest lead signals of the 12 lead ECG set.
It is known that the signals representing the respective ECG lead signals contain mutually redundant information. It is also known that, should one electrode be missing or malfunctioning, an appropriate combination of signals from the other electrodes and/or the other leads, which are available and functional, may be used to generate a synthesized signal which closely approximates the lead signal derived from the missing or malfunctioning electrode. To apply this technique, at least some portion of a full 12 lead ECG is recorded, during an analysis phase. The recorded signals are then processed to generate a function, which may be applied to the lead signals which are available, to synthesize a lead signal which approximates the lead signal which is missing or distorted beyond use. During a synthesis phase, this function is then applied to the available ECG lead signals. Using this technique, a missing lead may be synthesized. However the technique involves the disadvantages of being relatively complex and time consuming to perform. It is desirable to provide an ECG chest lead signal synthesis system that is capable of relatively quickly and simply synthesizing chest lead signals.